Belt tensioner with installation pin

ABSTRACT

A belt tensioner for tensioning the belt of a belt drive system includes an eccentric adjusting member, a pivot structure eccentrically mounted on the adjusting member for pivoting around the adjusting member, a belt-tensioning pulley mounted to rotate on the pivot structure, a biasing member that resiliently biases the pivot structure in a belt-tightening direction, and a coupling structure. The coupling structure temporarily couples the pivot structure to the adjusting member to pivot with it during a belt installation procedure, and the configuration keeps the coupling structure unloaded except for a limited period of time during the installation procedure such that the coupling structure can be installed and removed easily. The tensioner is rendered operative after the pivot structure is uncoupled from the adjusting member, thus allowing the pivot structure to pivot with respect to the adjusting member.

FIELD OF THE INVENTION

[0001] The present invention relates to belt tensioners and, inparticular, to belt tensioners that can be installed more easily andprecisely as part of an automotive belt drive system.

BACKGROUND OF THE INVENTION

[0002] Belt tensioners are generally well known devices that have beenused previously in many belt-drive systems. It is conventional practiceto use a tensioner to apply a constant belt-tensioning force, whichcompensates for increases in belt length due to wear and other factors.A common type of conventional belt tensioner has a fixed structure and apivoted structure eccentrically mounted on the fixed structure by meansof a pivot assembly, and the pivoted structure has a belt-engagingpulley rotationally mounted on it. A coil spring surrounds the pivotassembly and has its ends connected between the fixed and pivotedstructures so as to bias the pivot structure in a belt take-updirection. As the pivoted structure moves from a position of minimumbelt take-up to a position of maximum belt take-up, the spring biasingforce decreases. Despite this varying spring force over the range oftensioner movement, substantially constant belt tension is maintained bythe tensioner. U.S. Pat. No. 4,473,362, for example, illustrates thesebasic principles.

[0003] Various techniques are currently used to properly install timingbelt tensioners on engines. One of the most commonly used techniques isto construct the tensioner with an eccentric adjusting member that formspart of the fixed structure; the eccentric adjusting member is rotatedaround the tensioner mounting bolt and thus moves the tensioner awayfrom the belt (to allow the belt to be routed into the drive system) ortowards the belt (to apply tension in the drive system). A typicalinstallation procedure when using the current standard design includesmounting the tensioner on the engine with the eccentric member in theextreme position away from the belt, routing the belt into the drivesystem, rotating the eccentric member towards the belt until thetensioner reaches the nominal operating position, and locking thetensioner with the mounting bolt.

[0004] Because the eccentric adjusting member is located within theperiphery of the tensioner pivot, its size is limited and the maximumlinear stroke of the tensioner into and out of the drive system(approximately equal to twice the eccentricity of the eccentric member)may be insufficient to allow for proper installation of the belt.Additionally, recent trends to increase the number of components in thetiming drive system and to increase the tolerance range on beltdimensions, as well as requirements from engine OEM's that belts frommore than one supplier (i.e., belts with different tolerances) can beused on the same timing drive system, make it very difficult for atensioner equipped with a regular eccentric member to have enoughinstallation travel to accommodate all situations.

[0005] In order to address situations where the installation strokeprovided by the above design does not sufficiently move the tensioneraway from the belt to allow the belt to be routed into the drive system,an improved design was developed to increase the installation stroke. Inparticular, in such improved design tensioners, an installation pinlocks the pivoted structure to a fixed portion of the tensioner assemblyat an extreme position away from the belt (known as the load stopposition). The pin is inserted through the pivoted structure into afixed component (e.g., base plate, shaft, front plate, etc.) andcounters the action of the spring biasing member (tending to force thepivoted structure toward the belt). The installation procedure using theenhanced design includes mounting the tensioner on the engine with theeccentric member in the extreme position away from the belt, routing thebelt into the drive system, releasing the pin, rotating the eccentricmember towards the belt until the tensioner reaches the nominaloperating position, and locking the tensioner in place with the mountingbolt. This improved design increases the amount of space available toinstall the belt by holding the pivot arm as far away from the belt aspossible.

[0006] A disadvantage of such “enhanced” design, however, is that thepin is loaded by the spring (because the pin is required to hold thepivot arm at the load stop position, away from the belt). As a result,it can require significant force to remove the pin from the arm and thefixed component, which makes pin removal (and hence the tensionerinstallation procedure) difficult. Furthermore, when the pin is removedand the pivoted structure is “released” to pivot freely, the pivotedstructure may pivot all the way into contact with the tensioner free armstop with significant impact force. Such impact force can damage theinternal components of the tensioner, particularly if the tensioner usesa high torque spring.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a belttensioner that is generally easier to install than prior art tensioners.In accordance with the principles of the present invention, thisobjective is achieved by providing a belt tensioner for tensioning adrive belt or timing belt of a belt drive system including an eccentricadjusting member, a pivot structure, a belt-tensioning pulley, a coiltorsion spring or other biasing member, and a coupling structure. Thecoupling structure may be delivered or provided by the tensionermanufacturer as part of the tensioner assembly or it may be fitted intothe tensioner assembly only later, as part of the actual tensionerinstallation process, e.g., by an automobile manufacturer.

[0008] The eccentric adjusting member is configured to be mounted on amounting surface of an engine frame. The eccentric adjusting member isadjustable in a first, belt-tightening direction and a second directionaway from the first, belt-tightening direction; the pivot structure iseccentrically mounted on the adjusting member and pivots around theadjusting member; the belt-tensioning pulley is rotationally mounted onthe pivot structure; and the coil torsion spring or other biasing memberresiliently biases the pivot structure in a belt-tightening direction.The coupling structure temporarily couples the pivot structure to theeccentric adjusting member so that the pivot structure rotates with theadjusting member during an installation procedure in which the eccentricadjusting member is rotated away from the belt in order to allow thedrive belt or timing belt to be installed into the belt drive system.Coupling the pivot structure to the eccentric adjusting member in thatmanner significantly increases the tensioner stroke away from the beltand therefore makes it easier to install the belt.

[0009] After the belt has been installed, the adjusting member isrotated back toward the belt until the pivot structure comes to restagainst the free arm stop and/or against the belt. When the pivotstructure comes to rest against the free arm stop and/or the belt, thestop and/or belt will become subjected to the spring load, so little orno spring load force will be transmitted to the coupling structurethrough the pivot structure. Therefore, the coupling member can beremoved from the tensioner relatively easily at that point in theinstallation process to render the tensioner operative. The tensioner isrendered operative by uncoupling the pivot structure from the adjustingmember, thus allowing the pivot structure to pivot around the eccentricadjusting member.

[0010] Thus, in accordance with another aspect of the present invention,the object of the invention is achieved by providing a method ofinstalling a belt tensioner for a belt drive system, which tensionerincludes an eccentric adjusting member; a pivot structure that iseccentrically mounted on the adjusting member and that pivots around theadjusting member; a belt-tensioning pulley that is rotationally mountedon the pivot structure; and a spring or other biasing member that biasesthe pivot structure in a belt-tensioning direction. The method includesinitially mounting the adjusting member on the motor vehicle engine,e.g., with a relatively loose fixing bolt or stud; pivoting theadjusting member and, because it is (or becomes) coupled with theadjusting member, the pivot structure away from the belt against thebiasing force of the biasing member; mounting the belt on the componentsof the belt drive system; moving the adjusting member so that the pivotstructure moves toward the belt and relieves biasing force in thebiasing member; uncoupling the pivot structure from the adjustingmember; moving the adjusting member so that the pulley engages the beltand causes the pivot structure to pivot in the opposite direction (i.e.,the direction away from the belt) against the biasing force of thebiasing member; and, after the tensioner has been set in a predeterminedtensioning relationship with the belt, tightening the fixing bolt orstud to fix the adjusting member in place.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings facilitate an understanding of thevarious embodiments of this invention. In such drawings,

[0012]FIG. 1 is a perspective view of a belt tensioner constructed inaccordance with one embodiment of the present invention;

[0013]FIG. 2 is a front plan view of the belt tensioner in accordancewith one embodiment of the present invention;

[0014]FIG. 3 is an exploded view of the belt tensioner in accordancewith one embodiment of the present invention;

[0015]FIG. 4 is a front plan view of the belt tensioner in accordancewith one embodiment of the present invention;

[0016]FIG. 5 is a cross-sectional view taken through line 5-5 in FIG. 4showing the belt tensioner in accordance with one embodiment of thepresent invention;

[0017]FIG. 6 is a cross-sectional view of the belt tensioner inaccordance with one embodiment of the present invention;

[0018]FIG. 7 is a perspective view of the belt tensioner in accordancewith one embodiment of the present invention with a portion removed tothereby illustrate the inner components of the belt tensioner;

[0019]FIGS. 8A-8C are front plan views illustrating the installationprocedure of the belt tensioner in accordance with one embodiment of thepresent invention;

[0020]FIGS. 9A-9C are rear plan views illustrating the installationprocedure of the belt tensioner in accordance with one embodiment of thepresent invention;

[0021]FIG. 10 is a front plan view illustrating the belt tensioner inaccordance with one embodiment of the present invention with the arm atthe free arm stop position and the adjusting member not engaged with theinstallation pin;

[0022]FIG. 11 is a front plan view of the belt tensioner in accordancewith one embodiment of the present invention with the arm at the loadstop position and the adjusting member engaged with the installation pinand in the extreme position away from the belt.

[0023]FIG. 12 is a diagram illustrating the tensioner installationkinematics without the pivot arm coupled to the eccentric adjustingmember; and

[0024]FIG. 13 is a diagram illustrating the tensioner installationkinematics initially without the pivot arm coupled to the eccentricadjusting member and then with the pivot arm coupled to the eccentricadjusting member, as per the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] As illustrated in the drawings, a belt tensioner 10 whichembodies the principles of the present invention mounted on an engineblock or frame 12 by a threaded fixing bolt 14 (shown in FIG. 5) and isin tensioning engagement with a drive or timing belt 16 (shown in FIGS.8 and 9). Alternatively, the engine block 12 may include a stud (notshown) extending from it on which the tensioner is mounted and to whichthe tensioner is secured by a nut. Other means of securing the tensioner10 to the engine block 12 are also contemplated.

[0026] The tensioner 10 includes an inner, eccentric adjusting member 18that is used to move the tensioner pivot structure (lever arm 46) towardand away from the belt 16. As illustrated, the eccentric adjustingmember 18 can have a nested, two-component configuration. In particular,the illustrated adjusting member 18 consists of an inner installationshaft 20 and a surrounding, generally sleeve-shaped pivot shaft 22,which are secured together with a friction fit. The installation shaft20 and the pivot shaft 22 are secured together after the othercomponents of the tensioner (i.e., the arm 46, the pulley, 86, the ballbearing assembly 88, the torsion spring 82, etc., which are described inmore detail below) have been assembled onto the pivot shaft 22.

[0027] The installation shaft 20 of the adjusting member 18 is generallycylindrical, with a main, body portion 24 and a longitudinal bore 26extending axially through it. As illustrated most clearly in FIG. 5, thefixing bolt 14 (or mounting stud) extends through the longitudinal bore26, and the adjusting member 18 (installation shaft 20) rotates aroundthe fixing bolt 14. More particularly, the longitudinal bore 26 isdisplaced laterally or radially relative to the central, longitudinalaxis 28 of the cylindrical, body portion 24 of the installation shaft20, and the distance between the axis of the longitudinal bore 26(fixing bolt 14) and the central, longitudinal axis 28 provides theadjustment eccentricity of the adjusting member 18. (Depending on theamount of eccentricity and the radii of the installation shaft 20 andthe longitudinal bore 26, the periphery of the longitudinal bore 26 may,as illustrated, be internally tangent or almost internally tangent tothe periphery of the body portion 24 of the installation shaft 20.)Accordingly, the installation shaft 20, and hence the eccentricadjusting member 18, pivots eccentrically around the fixing bolt 14.

[0028] In the illustrated embodiment, the installation shaft 20 also hasa cam-shaped, radially outwardly projecting flange 30 that preferably isformed integrally with, but which could also be formed separately fromand connected to, the main body portion 24 of the installation shaft.Preferably, the flange 30 is formed at the end of the body portion 24that is furthest from the engine block 12. A slot 32 or other suitableengaging feature (such as a protrusion) is formed in the exteriorperiphery of the flange 30; the slot 32 functions cooperatively with aremovable installation pin 34 as the coupling structure during a beltinstallation procedure in which the belt 16 is trained about thetensioner 10 and installed in the belt drive system, as described ingreater detail below. Together, the slot 32 and pin 34 form a lostmotion-type coupling between the working eccentric or pivot arm of thetensioner 10 and the eccentric adjusting member 18. Although a lostmotion-type coupling arrangement is specifically illustrated, anycoupling structure or arrangement that temporarily couples the arm 46 tothe eccentric adjusting member 18, such that the arm pivots with theeccentric adjusting member during the tensioner and belt installationprocedure, can be used.

[0029] The flange 30 also has openings 36, which openings 36 receive theprongs of an adjusting tool 98 (FIGS. 8 and 9) that is used to rotatethe eccentric adjusting member 18 (and hence the pivot structure) duringthe installation procedure.

[0030] As noted above, the pivot shaft 22 of the adjusting member 18 isgenerally sleeve-shaped, with a main, cylindrical portion 38 that has acylindrical bore 40 extending axially or longitudinally through it. Thecylindrical, main body portion 24 of the installation shaft 20 isreceived within the bore 40 of the pivot shaft 22 with a friction fit,and together the installation shaft 20 and the pivot shaft 22 form theeccentric adjusting member 18. Other two-piece eccentric adjustingmember geometries besides cylinder-in-cylinder are known in the art andmay be employed as well. Alternatively, if so desired, a single-piececonfiguration can be used for the eccentric adjusting member 18.

[0031] In the illustrated embodiment, the pivot shaft 22 also has anoutwardly projecting flange 42 that is positioned closest to the engineblock 12. As shown in FIG. 5, the end surface of the pivot shaft 22,e.g., the end the projecting flange 42, is disposed insurface-to-surface engagement with a mounting surface provided on theengine block 12. This mounting surface can be provided by the engineblock 12 itself, or by a bracket or the like fixed to the engine block12.

[0032] A working eccentric or lever arm 46 functions as the tensionerpivot structure. The lever arm 46 has a main cylindrical portion 48 witha cylindrical exterior surface around which the pulley 86 fits and abore 50 extending longitudinally through it. The lever arm 46 fitsaround the eccentric adjusting member 18, which fits within the bore 50,and rotates around the eccentric adjusting member 18. The bore 50 isdisplaced laterally or radially relative to the central, longitudinalaxis 47 (the pulley axis) of the main cylindrical portion 48 of the arm46. Accordingly, the arm 46 pivots eccentrically relative to theadjusting member 18 as it rotates around it. The distance between theaxis 47 of the arm 46 and the central, longitudinal axis 28 of thecylindrical, body portion 24 of the installation shaft 20 (the centralaxis of the eccentric adjusting member 18, around which the arm 46pivots) provides the working eccentricity of the tensioner. By couplingthe lever arm 46 (pivot structure) to the eccentric adjusting member 18during the installation procedure, the working eccentricity of the leverarm 46 is “added” to the adjustment eccentricity of the eccentricadjusting member 18 and the installation stroke of the tensioner isincreased significantly.

[0033] As further shown, a pivot bushing 44, made from PTFE or similaranti-friction material, is provided to limit friction between the leverarm 46 and the eccentric adjusting member 18. The pivot bushing is pressfit into the bore 50, making a tight fit with the interior surface 52 ofthe bore 50 so as to rotate with the lever arm 46. The pivot bushing 44makes a sliding or clearance fit around the eccentric adjusting member18 (the exterior surface of the pivot shaft 22), which allows the pivotstructure or lever arm 46 to pivot relatively smoothly andfrictionlessly around the eccentric adjusting member 18.

[0034] In the illustrated embodiment, an annular wall portion 54 isprovided and extends radially outwardly from between the oppositelongitudinal ends of the lever arm 46, generally closer to the endadjacent the engine block 12. An outer cylindrical wall portion 56extends from an outer periphery of the annular wall portion 54 towardsthe engine block 12, in generally concentric relation to an end portion58 of the lever arm 46 that is located closest to the engine block 12.

[0035] A radially projecting pointer 60 extends from the arm 46.Preferably, the pointer 60 extends from a relatively thicker portion ofthe cylindrical wall portion 56 closest to the engine block 12, althoughit may extend from a portion of the arm 46 furthest from the engineblock 12 or be formed as a protrusion on top of the arm. Variouslocations certainly are permissible. The pointer 60 is used to gauge ormonitor installation of the tensioner 10 to make certain that thetensioner 10 engages the belt 16 with a predetermined amount of staticbelt-load force during the initial set-up.

[0036] The arm 46 further has a pin hole 62 to receive the pin 34 duringthe installation procedure, which is explained in greater detail below.Together with the slot 32, the pin constitutes part of the temporarycoupling structure.

[0037] A base plate 64 is positioned adjacent the engine block 12 andhas a circular opening 66 which receives the end of the adjusting member18. In the illustrated embodiment, the base plate 64 engages the flange42 of the pivot shaft 22 such that the base plate 64 is held in slightlyspaced relation from the engine block 12. However, the base plate 64 maybe engaged with the adjusting member 18 in any other suitable manner.

[0038] The base plate 64 has a projecting extension portion 68 and aprojecting locating portion 70 that is used to position the tensioner onthe engine. The extension 68 extends radially outwardly beyond the outerradial surface of the pulley 86, so that the portions 68 can be clearlyseen when the tensioner 10 is being installed on the engine block 12 asillustrated most clearly in FIGS. 8-11. The extension portion 68 of thebase plate 64 also has a notch 72 located along its exterior periphery,and the notch is used to gauge the position of the pointer 60 and hencethe belt load force.

[0039] The base plate 64 further includes a bent tab portion 74, whichextends axially in a direction away from the engine block 12, as shownin FIG. 5. The bent tab portion 74 functions as a stop member, whichremains fixed during operation of the tensioner 10 and cooperates withstop surfaces 76 and 78 (shown in FIGS. 9A-9C) of the arm 46 to limitthe angular or pivotal position of the arm 46. The stop surfaces 76 and78 are opposing surfaces formed on opposite sides of an opening 80formed in the arm 46, as shown most clearly in FIGS. 9A-9C. The tabportion or stop member 74 of the base plate 64 engages the stop surfaces76 and 78 upon rotation of the arm 46 beyond a predetermined angularrange to limit the possible extent of pivotal movement of the arm 46about the eccentric adjusting member 18. The stop surface 76 provides afree arm stop, and the stop surface 78 provides a load stop. Morespecifically, engagement of the stop surface 76 with the stop member 74defines the free arm stop position, and engagement of the stop surface78 with the stop member 74 defines the load stop position.

[0040] Other base plate configurations are also known in the art. Forexample, a similar base plate-type structure could be provided at theopposite end of the tensioner, opposite to the engine block 12.Alternatively, the base plate could be eliminated altogether, dependingon the specific tensioner configuration. Moreover, the tensioner stops(free arm and load) can be provided by means other than a portion of abase plate and/or other than the ends of a slot in the pivot arm.Additionally, the load stop could be eliminated altogether.

[0041] In order to optimize the stroke-increasing effectiveness of theinvention, the temporary coupling structure (i.e., the position of theslot 32 in the eccentric adjusting member 18 and the position of the pin34 in the arm 46) should be configured and/or positioned such that theadjusting member 18 will be pivoted to its position of maximum distancefrom the belt at or approximately at the same time as the arm 46 reachesthe load stop position. Additionally, the installation shaft 18 may bepivoted away from the belt 16 in either the clockwise or thecounterclockwise direction; the specific direction, however, must bedetermined and set during the design process in order to properlyconfigure the coupling structure, i.e., the position of the pin 34 andthe slot 32.

[0042] A torsion spring 82 is connected between the base plate 64 andthe arm 46. More particularly, the spring 82 has a main portion 84coiled freely about the main body portion 48 of the pivot arm 46,generally near a portion of the adjusting member 18 that is positionedclosest to the engine block 12. The end of the torsion spring 82 closestto the engine block 12 engages a spring stop that may be fixed to thebase plate 64 or any other fixed structure, such as the engine block 12.The other end of the torsion spring 82 is connected to the arm 46. Theconnection between the other end of the torsion spring 82 and the arm 46is conventional and operates to bias the arm in a counter-clockwise(i.e., belt-engaging) direction about the adjusting member 18, as shownin FIGS. 8A-8C for the illustrated exemplary embodiment.

[0043] Pulley 86 is disposed annularly around the arm 46 in conventionalfashion. Preferably, the pulley 86 is rotationally mounted on the arm 46by means of a ball bearing assembly 88. The ball bearing assembly 88 ismounted between an inner cylindrical surface of the pulley 86 and anouter cylindrical surface of the arm 46. The pulley 86 provides anexterior annular surface 90, which is preferably smooth to engage thepreferably flat exterior surface of the poly-V or timing belt 16.

[0044] A spring support 92 may, as shown, be disposed generally withinthe confines of the main spring portion 84. If provided, the springsupport 92 constitutes a bearing member between the base plate 64 andthe end portion 58 of the arm 46.

[0045] Additionally, a thrust washer 94 provides a bearing memberbetween an opposite end of the lever arm 46 and the flange 30. Thethrust washer 94 has a hole 96 that receives the pin 34 (either duringtensioner assembly or during the installation operation), and thediameter of the hole 96 is smaller than the diameter of the pin 34.Thus, when the pin 34 is inserted through the thrust washer 94, theedges of the hole 96 deform slightly and retain the pin 34 while thetensioner is being transported prior to being installed on the engineblock 12. That feature may be eliminated if the pin 34 is not shippedtogether with the tensioner 10 (e.g., if the pin is integrated into theinstallation tool 98) and the pin 34 is first inserted into thetensioner 10 during installation, either as integrated with theinstallation tool 98 or as a separate component altogether.

[0046] Installation and operation of the belt tensioner 10 will now bedescribed. Initially, the locating portion 70 of the base plate 64 ispositioned within a slot S (as shown in FIG. 5) provided in the engineblock 12, and the fixing bolt 14 is loosely fitted into a threadedopening within the engine block 12. Because the fixing bolt 14 is notinitially tightened, the adjusting member 18 can be rotated or pivotedeccentrically around the fixing bolt 14, e.g., using an appropriateinstallation and adjusting tool 98 such as shown in FIGS. 8 and 9, whichengages the pair of openings 36 in the flange 30 of the installationshaft 20.

[0047] The belt 16 is routed on or around all pulleys/sprockets of thebelt drive system of the engine except for the last component for beltinstallation. Because of the position of the tensioner 10 on the engineblock 12, the tensioner 10 must be rotated or pivoted away from the belt16 in order to install the belt on or around the last component for beltinstallation.

[0048] During tensioner assembly, if it was not supplied with thetensioner, the removable pin 34 is inserted into the hole 62 in the arm46, passing through the slot 32 in the adjusting member 18 and the hole96 in the thrust washer 94. The slot 32 allows the eccentric adjustingmember 18 to rotate in both directions relative to the arm or pivotstructure 46 by a limited amount, thus providing a lost motion-type ofcoupling as noted above, and using a slot generally makes it easier andsimpler to insert the pin into the tensioner during tensioner assembly(or during the tensioner installation process, if the pin is notpre-provided).

[0049] A pair of prongs on the installation and adjusting tool 98 areinserted into the pair of openings 36 in the adjusting member 18, andthe installation and adjusting tool 98 is used to rotate the adjustingmember 18 so that the pulley 86 is pivoted away from the belt 16, asindicated by the arrow in FIG. 8A. As the eccentric adjusting member 18is pivoted further away from the belt, end surface 100 of the slot 32 inthe adjusting member 18 (as shown most clearly in FIGS. 10 and 11) willcontact the pin 34. When that contact occurs, the lever arm 46 will betemporarily coupled to the eccentric adjusting member 18. As theeccentric adjusting member 18 is pivoted further away from the belt, thearm 46 will rotate with the eccentric adjusting member from the free armstop position (as shown in FIGS. 10, 8A, and 9A) towards the load stopposition (as shown in FIGS. 11, 8B, and 9B). Because it is (temporarily)coupled to the eccentric adjusting member 18 by means of the pin 34, thearm 46 can be rotated through its operating range together with theeccentric adjusting member 18.

[0050] Rotation of the adjusting member 18 away from the belt 16 may becontinued until the arm 46 reaches the load stop position, as mostclearly shown in FIG. 11. Once the arm 46 reaches the load stop position(or prior to the arm 46 reaching the load stop position, if the systemgeometry permits it), the belt 16 is installed over the last componentof the belt drive system while the tensioner 10 is held in the load stopposition. Preferably, the tensioner is designed so that the arm 46reaches the load stop position at the same time (or approximately thesame time) as the adjusting member rotates to an angular position thatmoves the tensioner assembly as far from the belt as possible, i.e., ata point where the axis of eccentricity of the adjusting member isaligned with the belt load direction.

[0051] As noted above, the eccentricity of the lever arm 46 is “added”to the eccentricity of the eccentric adjusting member 18; thus, theoverall tensioner stroke is increased, and it will be significantlyeasier to install the belt 16 around the final component and into thebelt drive system than in the case of previous tensioner configurations.Thus, by engaging the arm 46 to the adjusting member 18 via the couplingpin 34, the arm 46 can be rotated, within its operating range, togetherwith the adjusting member. This significantly increases the length ofthe effective installation eccentric, which can be defined as thedistance between the pulley center axis and the mounting bolt axis, asillustrated FIGS. 12 and 13.

[0052] By way of example, for a tensioner assembly having aninstallation eccentricity of 5.0 millimeters and an arm eccentricity of4.5 millimeters, the active installation stroke (distance the pulleymoves laterally away from the belt) increases approximately three-fold,from 2.2 millimeters to 6.2 millimeters, over 80° of rotation of theeccentric adjusting member, of which approximately the first 15° is withthe pivot arm uncoupled and approximately the last 65° is with the pivotarm coupled to the adjusting member via the coupling structure (pin 34).This results in a more efficient design of the tensioner and eliminatesthe need to increase the adjusting member eccentricity to achieve thenecessary installation stroke, which, in turn, reduces potentialpackaging difficulties and tensioner cost.

[0053] This benefit is illustrated diagrammatically in FIGS. 12 and 13.As illustrated in FIG. 12, as the installation eccentric rotateseccentrically around the installation bolt or stud with the twocomponents not coupled together, the arm remains pressed against thefree arm stop by the torsion spring, and the mobile (active) componentsof the tensioner (arm, bearing, pulley, washers, etc.) do not moverelative to the fixed components (pivot shaft, base plate, etc.). Inother words, the only component that rotates effectively during suchuncoupled rotation of the adjusting member is the installation eccentric(installation shaft 20), which rotates inside of the pivot shaft 22 andaround the mounting bolt or stud; the pivot arm is simply “carriedalong” translationally by the adjusting member.

[0054] The trajectory of the arm is quasi-circular, with a trajectoryradius that is approximately equal to the length of the installationshaft eccentricity. As the installation eccentric rotatescounter-clockwise (for example), its position relative to the hub loaddirection increases by Δα. At the same time, assuming approximately puretranslational movement of the base plate and pivot arm, the angle βformed by the installation eccentric a and the tensioner working armeccentric b decreases by the same amount (for α>90°). As a result, theeffective installation eccentric e, which forms a triangle with theinstallation eccentric a and the working arm eccentric b and which is afunction of a and b and the angle between them β, decreases withincreased rotation of the installation shaft.

[0055] Mathematically expressed, where e₁ is the length of the effectiveinstallation eccentric at a first angular position α and e₂ is thelength of the effective installation eccentric at a second angularposition α+Δα,

e ₁ ² =a ₁ ² +b ₁ ²−2ab·cos β, and

e ₂ ² =a ₂ ² +b ₂ ²−2ab·cos (β−Δα).

[0056] Therefore, as Δα increases with increasing rotation of theeccentric adjusting member, (β−Δα) tends to 0 and cos (β−Δα) tends to 1.Thus, it will be appreciated that

e₂<e₁.

[0057] As α approaches 180°, the length e of the effective installationeccentric continues to decrease to the point that e becomes smaller thanthe installation eccentric a (e<a). As that phenomenon occurs, strokeefficiency of the installation eccentric (i.e., the amount by which theposition of the pulley center moves away from the belt in the hub loaddirection for each further degree of rotation of the eccentricinstallation adjusting member) tends to 0.

[0058] In contrast, coupling the pivot arm to the eccentric adjustingmember in accordance with the invention ensures that the workingeccentric b continues to contribute to the tensioner installation strokeas the eccentric adjusting member moves through its entire installationrange of motion, thereby eliminating such degradation or dissipation ofthe tensioner stroke efficiency. As illustrated in FIG. 13, once the pin34 comes into contact with the end surface 100 of the slot 32 in theeccentric adjusting member 18, that engagement locks the relativeposition of the adjusting member 18 and the arm 46. Accordingly, theangle β formed by the installation eccentric a and the arm b remainsconstant, regardless of the angle α defining the installation eccentricposition (assuming approximately pure translational movement of the baseplate and pivot arm). As a result, the effective length e of theinstallation eccentric remains constant, and the amount by which theposition of the pulley center changes in the hub load direction for eachfurther degree of rotation of the installation shaft (efficiency of theinstallation) decreases only marginally (due to the change in position),even as α approaches 180°.

[0059] Thus, the trajectory of the arm after the two components arecoupled is circular, with the radius of the circle being equal to theeffective installation eccentric e and given by the formula

e ² =a ² +b ²−2ab·cos β=constant.

[0060] In fact, after the two components are coupled together, all ofthe mobile components move together with the installation eccentricaround the mounting bolt axis, relative to the fixed components, therebyincreasing the effective length of the installation eccentric and theavailable installation travel.

[0061] Before the adjusting member 18 has been pivoted away from thebelt, when the arm 46 is at the free arm position and the adjustingmember 18 has not engaged the pin 34 as shown in FIG. 10, the force onthe pin 34 will be very small or virtually zero. However, once theadjusting member 18 has been pivoted far enough for it to engage orbecome coupled with the arm 46 (by virtue of the end surface 100 of theslot 32 engaging the pin 34), the arm 46 will be forced to rotate orpivot away from the belt along with the adjusting member 18. At thatpoint, the arm 46 will be forced to rotate against the restoring orbiasing force generated by the torsion spring 82, with the maximumspring load being generated when the arm 46 reaches the load stopposition. Thus, while the arm 46 is being rotated or pivoted away fromthe belt along with the eccentric adjusting member 18, the pin 34 willbe loaded by the biasing spring force as the torsion spring 82 resiststhat pivoting rotation away from the belt.

[0062] After the belt has been completely installed into the belt drivesystem and properly positioned, as indicated by the arrow in FIG. 8B,the adjusting member 18, and hence the arm 46, is rotated (or allowed torotate under the influence of the torsion spring 82) back in the beltdirection (e.g., clockwise, as illustrated). The adjusting member 18 ismoved towards the belt 16 until the arm comes to rest against the freearm stop and/or the pulley engages the belt. When the pivot structurecomes to rest against the free arm stop and/or the belt, the stop and/orbelt will become subjected to the spring load, so little or no springload force will be transmitted to the coupling structure through thepivot structure, and surface 100 of the slot 32 disengages from the pin34 at that point. Thus, at that point, the spring load on the pin 34will again be very small, if not zero, and the pin 34 can be removedfrom the tensioner quite easily. When the pin 34 is removed, arm 46 willbe able to rotate or pivot unrestrained relative to the adjusting member18, and the tensioner will be operative (although not yet completelyset).

[0063] Once the pin 34 has been removed from the tensioner, theadjusting member 18 is rotated toward the belt 16 so as to press thepulley 86 into tensioning engagement with the belt 16. The adjustingmember can be rotated either further back in the counter-clockwisedirection (the original toward-the-belt direction) to press the pulleyinto tensioning engagement with the belt 16 at a “low” position, or itcan be rotated once again in the clockwise direction (the originalaway-from-the-belt direction) by over 180° so as to press the pulleyinto tensioning engagement with the belt 16 at a “high” position. Whensufficient tension is applied to the belt 16, the opposing belt loadtorque, applied by the belt 16 through the arm 46, will overcome thespring torque applied by the torsion spring 82 to the arm 46, and thearm 46 will start to rotate or pivot in the opposite direction relativeto the adjusting member 18 (i.e., in the direction away from the belt16). At this rotational or angular position of the adjusting member 18and the arm 46, the torsion spring 82 is adjusted such that it appliesthe desired, predetermined static tensioning force to the belt 16. Inother words, the tensioner 10 will be at its nominal operating position,as illustrated in FIGS. 8C and 9C.

[0064] At this point, the fixing bolt 14 is tightened to secure theadjusting member 18 in place. The tensioner 10 has thus been installedwith the arm 46 free to pivot about the adjusting member 18 (but limitedin its range of rotation by the stops 76 and 78). When the belt 16slackens during engine operation, the torsion spring 82 forces the arm46 to rotate, and due to the eccentric configuration, the arm 46 pivotsto move the pulley toward the belt to take up belt slack. Conversely,when tension in the belt 16 increases during engine operation, the belt16 applies a load force to the pulley that causes the arm 46 rotate inthe opposite direction, against the biasing force of the torsion spring82.

[0065] The tensioner has now been installed with the appropriate amountof tension in the torsion spring 82 to apply the appropriate amount oftorque to the arm 46 to properly tension the belt 16. Because the stopmember 74 is pre-fixed, the installation adjustment is made primarily toset the proper static tensioning force on the belt 16, i.e., not to setthe position of the stops 76 and 78 relative to the stop member 74.Thus, the installation adjustment need only be made such that the stopmember 74 is located somewhere between the stops 76 and 78.

[0066] As noted above, the tensioner 10 of the present inventionincreases the active installation stroke, yet leaves the couplingstructure (the pin 34) unloaded for installation and removal. Adding thetravel of the arm 46 to the adjusting member stroke increases theoverall installation stroke by approximately 50% as compared to theinstallation stroke of just the adjusting member travel. However, thelength of installation stroke needed during belt installation isvariable and is adaptable to the engine tolerances and belt length.Thus, it is possible that, for some engine/belt combinations, theadditional installation stroke obtained by rotating the arm 46 towardsthe load stop position is only needed in part or is not even required atall. In those cases, it will not be necessary to rotate the adjustingmember 18 and the arm 46 completely (i.e., until the arm 46 reaches theload stop-position), but only until the belt 16 can be routed into thedrive system.

[0067] Furthermore, because the pin 34 is unloaded (i.e., spring loaddoes not act on the pin 34) except during coupled rotation of thetensioner arm 46 and the adjusting member 18, installing and removingthe pin 34 during tensioner assembly is significantly easier.Additionally, the potentially damaging impact of the tensioner armrotating suddenly all the way to the free arm position as the pin isremoved is avoided.

[0068] As an alternative configuration, it is contemplated that the pinhole/slot configuration can be reversed. In particular, it iscontemplated that the pin hole for the installation pin might be formedin the flange of the eccentric adjusting member and the slot might beformed in the pivot arm, as opposed to vice-versa as described above.That configuration would provide the same lost motion-type of couplingbetween the pivot arm and the eccentric adjusting member as describedabove.

[0069] It will thus be appreciated that the objectives of the presentinvention have been fully and effectively accomplished. The foregoingspecific embodiments have been provided to illustrate the structural andfunctional principles of the present invention and is not intended to belimiting. To the contrary, the present invention is intended toencompass all modifications, alterations, and substitutions within thescope of the appended claims.

What is claimed is:
 1. A belt tensioner for tensioning a drive belt ortiming belt of a belt drive system, said belt tensioner comprising: aneccentric adjusting member constructed and arranged to be mounted on anengine mounting surface, said eccentric adjusting member beingadjustable in a first, belt-tightening direction and a second directionaway from the first, belt-tightening direction when mounted on theengine mounting surface; a pivot structure mounted on said adjustingmember for eccentric pivoting movement; a belt-tensioning pulley mountedfor rotational movement on said pivot structure; a biasing memberresiliently biasing said pivot structure in a belt-tightening direction;and a temporary coupling structure that temporarily couples said pivotstructure to said eccentric adjusting member such that when saideccentric adjusting member is rotated in the second direction, away fromthe first, belt-tightening direction, as part of an installationprocedure to allow the drive belt or timing belt to be installed intothe belt drive system, said pivot structure moves with said eccentricadjusting member against the bias of said biasing member, and whereindecoupling of said pivot structure from said eccentric adjusting memberby removal of said coupling structure renders said tensioner operativeby enabling said pivot structure to pivot freely and eccentrically aboutsaid eccentric adjusting member.
 2. A belt tensioner according to claim1, wherein said temporary coupling structure comprises a removable pin.3. A belt tensioner according to claim 2, wherein one of said eccentricadjusting member and said pivot structure has a slot and the other ofsaid eccentric adjusting member and said pivot structure has a hole andsaid pin passes through said slot and fits into said hole, saidtensioner being configured such that an end of said slot engages saidpin to couple said pivot structure with said adjusting member as saideccentric adjusting member is rotated in said second direction, awayfrom said belt-tightening direction, during the installation procedure.4. A belt tensioner according to claim 3, wherein said slot is formed insaid eccentric adjusting member and said hole is formed in said pivotstructure.
 5. A belt tensioner according to claim 1, wherein saidtensioner is constructed such that said biasing member impartsrelatively little or no torsional load to said temporary coupling memberuntil said pivot structure moves with said eccentric adjusting memberduring said installation procedure.
 6. A belt tensioner according toclaim 3, wherein said tensioner is constructed such that said biasingmember imparts relatively little or no torsional load to said pin untilthe end of said slot engages said pin to couple said pivot structure tosaid eccentric adjusting member, at which point said pivot structuremoves with said eccentric adjusting member during said installationprocedure.
 7. A belt tensioner according to claim 1, wherein thetensioner is configured such that the drive belt or timing belt can beinstalled into the belt drive system most easily when said eccentricadjusting member is at an extreme position away from the belt and saidpivot structure is pivoted relative to said eccentric adjusting memberto a position corresponding to maximum load-caused deflection.
 8. A belttensioner according to claim 1, further comprising a base plate, whereinsaid biasing member is operatively disposed between said base plate andsaid pivot structure to bias said pivot structure in saidbelt-tightening direction.
 9. A belt tensioner according to claim 8,wherein when said tensioner is installed, said base plate is disposedadjacent the engine mounting surface.
 10. A belt tensioner according toclaim 1, further comprising a base plate, wherein said base plate has astop member portion, said pivot structure has a load stop and a free armstop, and engagement of said stop member portion of said base plate withsaid load stop defines a load stop position of said pivot structure andengagement of said stop member portion with said free arm stop defines afree arm stop position of said pivot structure.
 11. A belt tensioneraccording to claim 1, wherein said biasing member comprises a torsionspring.
 12. A belt tensioner according to claim 1, wherein saideccentric adjusting member comprises two nested components.
 13. A belttensioner according to claim 12, wherein said two nested componentscomprise two nested cylindrical shafts.
 14. A belt tensioner fortensioning a drive belt or timing belt of a belt drive system, said belttensioner comprising: an eccentric adjusting member constructed andarranged to be mounted on an engine mounting surface, said eccentricadjusting member being adjustable in a first, belt-tightening directionand a second direction away from the first, belt-tightening directionwhen mounted on the engine mounting surface; a pivot structure mountedon said adjusting member for eccentric pivoting movement; abelt-tensioning pulley mounted for rotational movement on said pivotstructure; and a biasing member resiliently biasing said pivot structurein a belt-tightening direction; wherein said tensioner is configured toreceive a temporary coupling structure that temporarily couples saidpivot structure to said eccentric adjusting member such that when saideccentric adjusting member is rotated in the second direction, away fromthe first, belt-tightening direction, as part of an installationprocedure to allow the drive belt or timing belt to be installed intothe belt drive system, said pivot structure moves with said eccentricadjusting member against the bias of said biasing member, and whereinremoval of said temporary coupling structure decouples said pivotstructure from said eccentric adjusting member to render said tensioneroperative by enabling said pivot structure to pivot freely andeccentrically about said eccentric adjusting member.
 15. A belttensioner according to claim 14, wherein said temporary couplingstructure comprises a removable pin and said tensioner is configured toreceive said pin.
 16. A belt tensioner according to claim 15, whereinone of said eccentric adjusting member and said pivot structure has aslot and the other of said eccentric adjusting member and said pivotstructure has a hole and said pin passes through said slot and fits intosaid hole, said tensioner being configured such that an end of said slotengages said pin to couple said pivot structure with said adjustingmember as said eccentric adjusting member is rotated in said seconddirection, away from said belt-tightening direction, during theinstallation procedure.
 17. A belt tensioner according to claim 16,wherein said slot is formed in said eccentric adjusting member and saidhole is formed in said pivot structure.
 18. A belt tensioner accordingto claim 14, wherein said tensioner is constructed such that saidbiasing member imparts relatively little or no torsional load to saidtemporary coupling member, when received by said tensioner, until saidpivot structure moves with said eccentric adjusting member during saidinstallation procedure.
 19. A belt tensioner according to claim 16,wherein said tensioner is constructed such that said biasing memberimparts relatively little or no torsional load to said pin, whenreceived by said tensioner, until the end of said slot engages said pinto couple said pivot structure to said eccentric adjusting member, atwhich point said pivot structure moves with said eccentric adjustingmember during said installation procedure.
 20. A belt tensioneraccording to claim 14, wherein the tensioner is configured such that,with said coupling member received by the tensioner, the drive belt ortiming belt can be installed into the belt drive system most easily whensaid eccentric adjusting member is at an extreme position away from thebelt and said pivot structure is pivoted relative to said eccentricadjusting member to a position corresponding to maximum load-causeddeflection.
 21. A belt tensioner according to claim 14, furthercomprising a base plate, wherein said biasing member is operativelydisposed between said base plate and said pivot structure to bias saidpivot structure in said belt-tightening direction.
 22. A belt tensioneraccording to claim 21, wherein when said tensioner is installed, saidbase plate is disposed adjacent the engine mounting surface.
 23. A belttensioner according to claim 14, further comprising a base plate,wherein said base plate has a stop member portion, said pivot structurehas a load stop and a free arm stop, and engagement of said stop memberportion of said base plate with said load stop defines a load stopposition of said pivot structure and engagement of said stop memberportion with said free arm stop defines a free arm stop position of saidpivot structure.
 24. A belt tensioner according to claim 14, whereinsaid biasing member comprises a torsion spring.
 25. A belt tensioneraccording to claim 14, wherein said eccentric adjusting member comprisestwo nested components.
 26. A belt tensioner according to claim 25,wherein said two nested components comprise two nested cylindricalshafts.
 27. A method of installing a belt tensioner in a motor vehiclebelt drive system, said tensioner comprising an eccentric adjustingmember, a pivot structure mounted on the adjusting member for eccentricpivoting movement, a belt-tensioning pulley mounted for rotation on thepivot structure, and a biasing member that biases the pivot structure ina first direction that is toward the belt drive system belt to force thepulley into tensioning engagement with the belt when the tensioner isinstalled on the motor vehicle engine, said method comprising: initiallymounting the tensioner on the motor vehicle engine by means of a bolt orstud around which the eccentric adjusting member pivots; pivoting theeccentric adjusting member and, while the pivot structure is coupledwith the eccentric adjusting member, the pivot structure so that thepivot structure is moved in a second direction, away from the firstdirection, against the biasing force of the biasing member; mounting thebelt on or around all components of the belt drive system; pivoting theeccentric adjusting member back in the first direction so that the pivotstructure is moved back in the first direction, toward the belt, and sothat biasing force in the biasing member is relieved; decoupling thepivot structure from the eccentric adjusting member; pivoting theeccentric adjusting member so that the pulley is pressed into forcibleengagement with the belt, thereby causing pivoting movement of the pivotstructure against the biasing force of the biasing member; andtightening the bolt or stud so as to fix the adjusting member, and hencethe tensioner, in place after the pivot structure has been pivoted intoa predetermined tensioning position relative to the belt.
 28. The methodof claim 27, wherein said eccentric adjusting member is pivoted in saidsecond direction, away from the belt, by a predetermined initial angularextent before said pivot structure becomes coupled to said eccentricadjusting member.
 29. The method of claim 28, wherein said couplingstructure remains unloaded while said eccentric adjusting member isbeing pivoted through said predetermined initial angular extent andbecomes loaded only after said pivot structure and said eccentricadjusting member become coupled and said eccentric adjusting member ispivoted beyond said predetermined initial angular extent.
 30. The methodaccording to claim 28, wherein the eccentric adjusting member and thepivot structure are coupled by means of a lost motion-type couplingconfiguration comprising a hole in the, pivot structure, a pin whichfits into the hole, and a slot in the eccentric adjusting member throughwhich the pin passes and within which the pin slides, wherein thepredetermined initial angular extent is delimited by an end of the slotengaging the pin during pivoting of the eccentric adjusting member inthe second direction, away from the belt, said engaging thereby couplingthe pivot structure to the adjusting member, and wherein the pivotstructure becomes decoupled from the eccentric adjusting member when theend of the slot disengages from the pin during said pivoting of theeccentric adjusting member back in the first direction.
 31. The methodof claim 30, further comprising removing the pin from the tensioner whenthe pivot structure becomes decoupled from the eccentric adjustingmember by the end of the slot disengaging from the pin, thereby allowingthe pivot member to pivot relative to the eccentric adjusting member,unrestrained by the pin.
 32. The method according to claim 27, whereinthe pivot arm is pivoted in said second direction, away from the belt,to an extreme, load stop position substantially at the same time as saideccentric adjusting member is pivoted in said second direction to amaximum distance away from the belt.
 33. The method of claim 31, whereinsaid belt is mounted on or around all of the components of the beltdrive system when the pivot arm is pivoted to the extreme, load stopposition and the eccentric adjusting member is pivoted to the maximumdistance away from the belt.